Diaphragm for loudspeakers

ABSTRACT

A diaphragm for a loudspeaker made of foamed plastic or like material, in which the diaphragm has a decreased thickness at its central portion to which a voice coil is attached.

United States Patent lllroml Somme lhmlmntsu-shi, Japan Mar. 3, 1969 June 22, 1971 Nippon Gakki Seito Kabushiki Kalsha Hamamatsu-shi, Japan inventor Appl. No. Filed Patented Assignee DIAPHRAGM F011 wunsrmxnas 1 Claim, 9 Drawing Fig.

11.8. C1. 181/32 Int. Cl 610k 13/00, H04r 7/00 FleldolSeareh 181/32,31, 31.1

[56] References Cited UNITED STATES PATENTS 1,832,832 11/1931 Nagelvoort 181/32 1,872,081 8/1932 l-lawley 181/32 2,200,490 5/1940 Cornwell 181/31 2,905,260 9/1959 Williams... 181/32 3,153,463 10/1964 Novak 181/32 Primary Examiner-Stephen .1 Tomsky Attorney-Stevens, Davis, Miller and Mosher ABSTRACT: A diaphragm for a loudspeaker made of foamed plastic or like material, in which the diaphragm has a decreased thickness at its central portion to which a voice coil is attached.

PATENTED M22 1% FIGLIA 'FIVG. IB"

FIG. IE

INVENTOR HIM/11 JOTO/{ mmm m ATTORNEYJ ammo son LOUDSPEAKERS BACKGROUND OF THE INVENTION The present invention relates to a diaphragm for a loudspeaker made of foamed plastic or like material.

l-leretofore a number of types of diaphragm made of foamed plastic such as foamed polystyrene or like material have been proposed. FIGS. 1 A, B, C, D and E illustrate some examples of such diaphragm. FIG. 1A shows a diaphragm made of a flat plate Ia having uniform thickness of foamed plastic material such as foamed polystyrene and having a voice coil 2a attached to its central portion. FIG. 1B shows a diaphragm made of a flat plate lb having a thickness increasing stepwise toward its central portion to which a voice coil 2b is attached. FIG. 1C shows a diaphragm made of a flat plate Ic having a thickness increasing gradually toward its central portion to which a voice coil 20 is attached. FIG. ID shows a diaphragm made of a plate 1d having uniform thickness which is formed in a cone having an apex portion to which a voice coil 2d is attached. FIG. 1B shows a diaphragm made of a flat plate which is formed at its central area in a gradually curved conical form, to which a voice coil 2: is attached.

These diaphragms can faithfully reproduce low frequency sounds and their frequency characteristics in the low frequency range depend on piston motion or on overall bending (fundamental single bending) motion of the diaphragm. However, in the medium or high frequency ranges, the diaphragms tend to produce divided vibrations, resulting in peaks and dips in their frequency characteristics. Consequently, a smooth frequency characteristic such as in a conventional cone-type loudspeaker using a cone paper diaphragm cannot be obtained in these diaphragms. Furthermore, these diaphragms have relatively increased mass at the central portion, so that they cannot satisfactorily reproduce higher frequency sounds.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a diaphragm for a loudspeaker made of foamed plastic or like material which can reproduce effectively high frequency sounds as well as low frequency sounds.

Itis another object of the present invention to provide a diaphragm for a loudspeaker made of foamed plastic or like material in which a flat or smooth frequency characteristic curve can be obtained throughout whole range from low frequency to high frequency.

In accordance with the present invention there is provided a diaphragm for a loudspeaker made of foamed plastic or like material in which the diaphragm has a decreased thickness at its central portion to which a voice coil is attached.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 A, B, C, D and E are sections showing examples of a conventional loudspeaker diaphragm;

FIGS. 2, 3, 4 and 5 are sectional views showing several embodiments of the diaphragm according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIGS. 2,3, 4 and 5 illustrate some embodiments of the present invention.

FIG. 2 shows a first embodiment in which a diaphragm is made of a flat plate 34 of foamed plastic material which hasa decreased thickness at its central portion 4a, to which a voice coil 5a is attached. The diaphragm shown in FIG. 2 can reproduce high frequency sound, but has some defect in that it lacks rigidity at the central portion so that deep dips may occur in the frequency characteristic in its low frequency ran e.

l G. 3 shows a second and most preferred embodiment of so as to gradually increase its rigidit at its central area, In this central area the plate 3b gra ual y decreases its thickness toward the central portion 4b to which a voice coil 5b is attached, thereby decreasing mass of effective vibrating area which contributes to the vibration of the diaphragm at high frequency rage.

FIG. 4 shows a third embodiment of the present invention, in which a diaphragm is made of a flat plate 3c of foamed plastic or like material which is formed in a gradually curved conical shape at its central area, as in the embodiment shown in FIG. 3. The plate 3c has a thick part 6 at the peripheral portion of the conical area where the angle of inclination is relatively small, said thick part 6 serving to increase the rigidity of the plate to improve the frequency characteristics in the low frequency range. The plate 3c gradually decreases its thickness from the thick part 6 toward a central portion 4c where the angle of inclination is increased, to which a voice coil 5 is attached. In such a construction, the plate has a relatively high rigidity in the central portion owing to its conical shape although the thickness is decreased toward the central portion, so that characteristic in the low frequency range is not adversely afiected by the decrease of the thickness. Furthermore, while the level in medium frequency range generally tends to be increased by forming the plate in the conical shape, excessive increase in level is prevented owing to the increase of vibrating mass in the medium frequency range by the thick part 6. Thus a relatively flat or smooth characteristic curve can be obtained through low frequency sound to high frequency sound.

FIG. 5 shows a fourth embodiment of the present invention in which a diaphragm is made of a flat plate 3d of foamed plastic material, which has a free edge 7. at its periphery, through which the plate is supported by a frame (not shown). A central portion 4d of the plate has similar construction as shown in FIG. 3, and a voice coil 5d is attached to said central portion.

The following table shows two examples of the diaphragm constructed in accordance with the present invention.

Size of Thickness Thickness at diaphragm at periphery central portion 800 X 500mm 7mm 3mm 400 X 320mm 3mm 2mm Of course, the thickness may be above description determined, depending on the size of the diaphragm, the material of the diaphragm or the desired characteristics.

It will be understood from the above-description that in accordance with the present invention sounds can be effectively reproduced throughout whole range from low frequency to high frequency with a flat or smooth frequency characteristic, by a diaphragm made of foamed plastic or like material which could not heretofore live a flat frequency characteristic.

I claim:

I. In a diaphragm for a loudspeaker, said diaphragm comprising a member the major portion of which is substantially planar and of substantially uniform thickness foamed plastic and said diaphragm having a voice coil attached thereto, the improvement which comprises providing in the central portion of said member an indentation of curved conical shape, the angle of inclination of the walls of said conical indentation with respect to the diaphragm axis gradually increasing as the apex of the conical shape is approached, the walls of said curved conical indentation having a peripheral portion adjacent to and thicker than said major portion and then gradually decreasing in thickness toward said apex, and said voice coil being attached to said apex. 

1. In a diaphragm for a loudspeaker, said diaphragm comprising a member the major portion of which is substantially planar and of substantially uniform thickness foamed plastic and said diaphragm having a voice coil attached thereto, the improvement which comprises providing in the central portion of said member an indentation of curved conical shape, the angle of inclination of the walls of said conical indentation with respect to the diaphragm axis gradually increasing as the apex of the conical shape is approached, the walls of said curved conical indentation having a peripheral portion adjacent to and thicker than said major portion and then gradually decreasing in thickness toward said apex, and said voice coil being attached to said apex. 